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theories of dominance

Brain Foley brianf at dna.uvm.edu
Wed Mar 24 16:09:49 EST 1993

I was mislead earlier, in part because I was not familiar with the way
in which you use the terms "dominance" and "recessive".  In my
training, "dominant" means only that one copy of the gene will produce
the phenotype being looked at (i.e. yellow/green heterozygote pea pods
will be green; green is dominant over yellow), it says nothing about
whether the dominant or recessive allele provides better "fitness".

It is in this regard that I feel that new knowledge has changed the
way we should look at genetics.  Using green and yellow pods as an
example, we might now find out that yellow peas lack the gene for
green pigments, or we might find out that they produce a yellow
pigment.  Using visual analysis, green is the dominant gene, but using
an assay that detects only yellow pigments, yellow is the dominant
gene.  This is where I have a problem: dominance or recesiveness in
these cases is in the eye of the beholder.

Many students in molecular genetics are confused about what "dominant"
and "recesive" mean.  Most often, recessive means that some gene
product is lacking, so if a cell-cell hybrid is made, the cell with
the dominant phenotype provides the lacking enzyme.  But this is not
always the case.

I guess I was sticking my neck out to post to molbio.evolution when I
am not a student of population biology, but I think that is important
for all biologists to use the same definitions for the same terms.  I
think that "dominant" can be a fuzzy term in some cases now.
*  Brian Foley               *     If we knew what we were doing   *
*  Molecular Genetics Dept.  *     it wouldn't be called research  *
*  University of Vermont     *                                     *

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